This invention relates to the field of reducing radiant energy noise signals arising from laser use, for example, target designating laser use, within the cockpit of a military aircraft. The invention supports concuteat operation of such lasers with night vision equipment and visual flight practices.
According to current states of the warfare and technical arts combat aircraft crewmembers often use portable infrared lasers to designate certain classes of ground targets for munitions reception. In this practice a crewmember holds a target designating laser by hand and in the case of a single crew member tactical aircraft, simultaneously flies the aircraft. This activity is often accomplished while also wearing both night vision goggles and laser eye protection apparatus. Currently, low power infrared lasers are often used for such target designation purposes. A desirable increase in aircraft to target standoff range and other advantages can however be realized through use of more powerful lasers in this service. Current target designating lasers are largely of the solid state type; with use of the instant invention however, a spurious laser energy return phenomenon and a resulting night vision difficulty, which presently limit the desirability of higher powered lasers as target designators, are eliminated and higher powered lasers and possibly gaseous lasers become more attractive for target designation.
A difficulty encountered with both current and such contemplated future use of this target designating practice originates in the fact that materials used in aircraft canopies when acting as a laser energy transmitting medium are not free of energy losses and attending complexities. In fact, canopy materials when acting as a laser light conduit tend to produce a significant veiling canopy glow phenomenon. The canopy glow phenomenon arises from internal imperfections (particulate inclusions and bubbles) found within the canopy material and from exterior surface imperfections (such as scratches, abrasions and sand or stone impact marks) on the canopy surface. The canopy glow phenomenon is thus primarily due to imperfection-induced total internal reflections and Fresnel internal reflections causing a conduit effect loss over a significant part of the canopy surface. This veiling canopy glow or canopy glow-sourced radiant energy may be considered an infrared noise signal and significantly interferes with the aircraft crew""s out-of-cockpit night vision goggle-aided vision; the vision needed for aircraft flight control and for target acquisition and designation. In general the veiling canopy glow causes excessive signal input, blooming and distant object hiding effects in the night vision equipment and increases in severity as laser power increases. Usually however this canopy glow is not accompanied by direct or first order heat effects since the laser energy involved preferably resides in the short rather than long infrared wavelength part of the electromagnetic spectrum. Laser light from the target designator also can bounce around the aircraft cockpit and necessitate the crewmembers wearing laser eye protection gear. This same laser eye protection gear can however reduce night vision goggle visual performance.
The present invention provides reduced spurious radiant energy returns from the interior and exterior portions of transparent optical materials used to close aircraft fuselage openings when these materials are energized by a high energy source of radiation such as a laser. The invention is particularly useful in the case of target designation by portable laser from within a night vision system-equipped tactical military aircraft cockpit.
It is an object of the present invention therefore, to enhance the night operation capability of a military aircraft.
It is another object of the invention to enable night vision system-compatible usage of a laser target designating apparatus in an aircraft cockpit.
It is another object of the invention to reduced energy reflections, veiling canopy glow and other spurious energy returns encountered during use of a laser target designating apparatus in an aircraft cockpit.
It is another object of the invention to provide a laser window apparatus of low spurious energy return characteristics.
It is another object of the invention to simplify the use of higher power target designating lasers within an aircraft cockpit.
It is another object of the invention to provide an uninterrupted flow of visual information to a pilot or air crew member during operation of a laser target designating apparatus.
It is another object of the invention to preclude age degradation effects attending laser energy transmission through the materials of an aircraft canopy.
It is another object of the invention to provide an easily replaced canopy region usable for laser energy transmission from an aircraft.
It is another object of the invention to limit the laser related effects of aircraft windshield defects.
It is another object of the invention to limit or eliminate a significant source of night vision apparatus saturation and recovery time effects in an aircraft cockpit.
It is another object of the invention to attenuate the total internal reflection, Fresnel reflection and scatter related effects accompanying laser energy transmission through transparent materials.
It is another object of the invention to attenuate the laser illuminated effects of material defects such as bubbles, particulate inclusions and surface defects in aircraft windshield or canopy materials.
It is another object of the invention to reduce laser eye damage possibilities in the cockpit of an aircraft.
It is another object of the invention to enhance the aircraft to target standoff distance capability of a laser inclusive airborne military weapons system.
It is another object of the invention to enable the increased standoff range between a target designating aircraft and its target by increased laser operating power levels.
It is another object of the invention to enable the use of differing laser types and differing operating wavelengths in target designating apparatus.
It is another object of the invention to enable the use of lasers of differing spectral capability and energy level in aircraft target designator apparatus.
It is another object of the invention to provide a plurality of physical arrangements usable in disposing a laser window apparatus in an aircraft and its transparency.
It is another object of the invention to provide a laser window apparatus usable in a variety of aircraft windshield and canopy arrangements.
It is another object of the invention to provide reduced infrared signature from the cockpit of an aircraft during use of cockpit laser apparatus.
It is another object of the invention to increase the effectiveness of hand held lasers used by combat aircraft crews to designate certain ground targets.
It is another object of the invention to provide enhanced visibility of an aircraft-sourced laser target designation from other aircraft.
It is another object of the invention to compensate for the effects of canopy wear (such as abrasions, scratches and so-on) on the use of laser target designation.
These and other objects of the invention are achieved by laser path window apparatus comprising the combination of:
a first radiant energy transmission member having radiant energy transmission capability in both thickness first and thickness-orthogonal second directions;
a second radiant energy transparent member physically smaller in said thickness-orthogonal direction than said first optically transparent member and having loss-inclusive radiant energy transmission capability in both thickness and thickness-orthogonal directions;
said second radiant energy transparent member being coplanar received in a to selected thickness-orthogonal direction region of said first radiant energy transmission member;
a laser member having radiant output energy directed through said second radiant energy transparent member in said thickness direction;
said loss inclusive radiant energy transmission capability in said second radiant energy transparent member generating, from said thickness direction-oriented laser radiant output energy, energy loss portions having a thickness-orthogonal direction component of orientation;
a geometrically closed radiant energy containment member surrounding said smaller second radiant energy transparent member in said thickness-orthogonal direction and interrupting said radiant energy loss portions having a thickness-orthogonal direction component of orientation intermediate said smaller second radiant energy transparent member and said surrounding first radiant energy transmission member;
said interrupting and said geometrically closed radiant energy containment member limiting radiant energy loss portion-sourced spurious energy emissions from said laser path window apparatus to occurrence in portions of said second radiant energy transparent member in exclusion of said first radiant energy transmission member.